1. Field of the Invention
The present invention relates to a disk drive and a write control method for the disk drive. More particularly, the present invention relates to a disk drive and a write control method for the disk drive which reduces the number of unnecessary write inhibition operations.
2. Description of Related Art
Conventional hard-disk drives include one or more magnetic disks with concentrically formed circular tracks. The reading of information from the magnetic disk or the writing of information to the magnetic disk is performed after a seek operation. A seek operation moves a magnetic head in the radial direction of the magnetic disk to position the head over the desired track on the disk. During a seek operation, the head position identification information previously recorded of a predetermined area on the magnetic disk is read by the magnetic head in order to position the magnetic head over the desired track, while confirming the current position of the magnetic head. More specifically, during a seek operation, the positioning of the magnetic head is performed while the head position on a disk is confirmed based on the regenerative output of the servo sector recorded on a servo area.
When positioning the magnetic head over a desired track on the disk, the current position of the magnetic head is detected based on the regenerative output of the identification information which is regenerated by the magnetic head each time it is positioned over an identification information storage area. Then, if it is determined that the magnetic head has arrived at the desired track, a position (error) detection signal, which has a level that varies linearly in correspondence with the position of the magnetic head, is produced based on the regenerated signal from a burst pattern storage area. Furthermore, based on the position detection signal, the magnetic head is controlled so that it is positioned over the center (i.e., in the width direction) of the desired data track.
If a write operation is performed at an off-track position considerably removed from the center position of the desired track, the data stored on an adjacent track may be destroyed. For this reason, it is desirable to have a method for detecting whether or not the magnetic head is in the off-track state in order to inhibit a write operation when such a state exits.
For a sector servo type of hard-disk drive, a first criteria for determining an error in the head position is provided such that if the error in the head position exceeds this first criteria, then a write operation is inhibited. Furthermore, in a hard-disk drive such as this, a second criteria for the velocity in the track width direction of the magnetic head is also provided. If the velocity in the track width direction of the head exceeds the second criteria, a write operation is inhibited.
Immediately after the settling of the head during a seek operation, the vibration of the head actuator arm resulting from the seek operation is not attenuated thereby causing the position in the track width direction of the head to be unstable. For this reason, the criteria for the head velocity in the track width direction is set to take the most unstable state immediately after the settling of the head. This effectively prevents a write operation in the off-track state immediately after the settling.
For the invention disclosed in Published Unexamined Patent Application No. 8-321149 (Patent Application No. 7-124698), a read characteristic is changed for a fixed amount of time after the end of a seek operation. More specifically, the readable range in the track width direction is narrowed. Consequently, the write inhibition conditions after the end of a seek operation are made rigorous.
When writing the aforementioned tracking patterns on the magnetic disk, non-repeatable runout (NRRO) due to vibration, which has no regularity with respect to rotation of the spindle motor, may occur at the position in which the tracking pattern is written. Additionally, a microscopic defect may occur on a data storage medium (magnetic disk). NRRO and/or medium defects, often create a fluctuation in the position error signal PES of the head, even if there is no actual displacement in the head actuator arm when the tracking pattern is regenerated.
If the fluctuation in the head position or fluctuation in the velocity of the magnetic head in the track width direction is greater than the first and second criteria described above, a write operation is inhibited. In the case where the position error signal PES is increased by fluctuation independent of the displacement of the head actuator arm after a short time has elapsed from the settling of the head against the disk, the head is not considered to be moved too far from the original track position. Therefore, after a short time has elapsed from the settling of the head, a slight increase in the PES is considered negligible.
In the case where the criteria for the head velocity in the track width direction is set to take into consideration the state immediately after the settling of the head, the criteria is too strict with respect to the fluctuation in the PES after a short time from the settling of the head. Consequently, unnecessary write inhibit operations are frequently performed. This often degrades the write performance of the drive.